Isotopes of rubidium

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Rubidium (Rb) has 24 isotopes, with naturally occurring rubidium being composed of just two isotopes; Rb-85 (72.2%) and the radioactive Rb-87 (27.8%). Normal mixes of rubidium are radioactive enough to fog photographic film in approximately 30 to 60 days. Standard atomic mass is 85.4678(3) u

Rb-87 has a half-life of 4.88×10¹⁰ years. It readily substitutes for potassium in minerals, and is therefore fairly widespread. Rb has been used extensively in dating rocks; Rb-87 decays to stable strontium-87 by emission of a negative beta particle. During fractional crystallization, Sr tends to become concentrated in plagioclase, leaving Rb in the liquid phase. Hence, the Rb/Sr ratio in residual magma may increase over time, resulting in rocks with increasing Rb/Sr ratios with increasing differentiation. Highest ratios (10 or higher) occur in pegmatites. If the initial amount of Sr is known or can be extrapolated, the age can be determined by measurement of the Rb and Sr concentrations and the Sr-87/Sr-86 ratio. The dates indicate the true age of the minerals only if the rocks have not been subsequently altered. See rubidium-strontium dating for a more detailed discussion.

[edit] Table

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
nuclide symbol	excitation energy			half-life	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
⁷¹Rb	37	34	70.96532(54)#		5/2-#
⁷²Rb	37	35	71.95908(54)#	<1.5 µs	3+#
^72mRb	100(100)# keV			1# µs	1-#
⁷³Rb	37	36	72.95056(16)#	<30 ns	3/2-#
⁷⁴Rb	37	37	73.944265(4)	64.76(3) ms	(0+)
⁷⁵Rb	37	38	74.938570(8)	19.0(12) s	(3/2-)
⁷⁶Rb	37	39	75.9350722(20)	36.5(6) s	1(-)
^76mRb	316.93(8) keV			3.050(7) µs	(4+)
⁷⁷Rb	37	40	76.930408(8)	3.77(4) min	3/2-
⁷⁸Rb	37	41	77.928141(8)	17.66(8) min	0(+)
^78mRb	111.20(10) keV			5.74(5) min	4(-)
⁷⁹Rb	37	42	78.923989(6)	22.9(5) min	5/2+
⁸⁰Rb	37	43	79.922519(7)	33.4(7) s	1+
^80mRb	494.4(5) keV			1.6(2) µs	6+
⁸¹Rb	37	44	80.918996(6)	4.570(4) h	3/2-
^81mRb	86.31(7) keV			30.5(3) min	9/2+
⁸²Rb	37	45	81.9182086(30)	1.273(2) min	1+
^82mRb	69.0(15) keV			6.472(5) h	5-
⁸³Rb	37	46	82.915110(6)	86.2(1) d	5/2-
^83mRb	42.11(4) keV			7.8(7) ms	9/2+
⁸⁴Rb	37	47	83.914385(3)	33.1(1) d	2-
^84mRb	463.62(9) keV			20.26(4) min	6-
⁸⁵Rb	37	48	84.911789738(12)	STABLE	5/2-	0.7217(2)
⁸⁶Rb	37	49	85.91116742(21)	18.642(18) d	2-
^86mRb	556.05(18) keV			1.017(3) min	6-
⁸⁷Rb	37	50	86.909180527(13)	4.923(22)E+10 a	3/2-	0.2783(2)
⁸⁸Rb	37	51	87.91131559(17)	17.773(11) min	2-
⁸⁹Rb	37	52	88.912278(6)	15.15(12) min	3/2-
⁹⁰Rb	37	53	89.914802(7)	158(5) s	0-
^90mRb	106.90(3) keV			258(4) s	3-
⁹¹Rb	37	54	90.916537(9)	58.4(4) s	3/2(-)
⁹²Rb	37	55	91.919729(7)	4.492(20) s	0-
⁹³Rb	37	56	92.922042(8)	5.84(2) s	5/2-
^93mRb	253.38(3) keV			57(15) µs	(3/2-,5/2-)
⁹⁴Rb	37	57	93.926405(9)	2.702(5) s	3(-)
⁹⁵Rb	37	58	94.929303(23)	377.5(8) ms	5/2-
⁹⁶Rb	37	59	95.93427(3)	202.8(33) ms	2+
^96mRb	0(200)# keV			200# ms [>1 ms]	1(-#)
⁹⁷Rb	37	60	96.93735(3)	169.9(7) ms	3/2+
⁹⁸Rb	37	61	97.94179(5)	114(5) ms	(0,1)(-#)
^98mRb	290(130) keV			96(3) ms	(3,4)(+#)
⁹⁹Rb	37	62	98.94538(13)	50.3(7) ms	(5/2+)
¹⁰⁰Rb	37	63	99.94987(32)#	51(8) ms	(3+)
¹⁰¹Rb	37	64	100.95320(18)	32(5) ms	(3/2+)#
¹⁰²Rb	37	65	101.95887(54)#	37(5) ms

[edit] Notes

Geologically exceptional samples are known in which the isotopic composition lies outside the reported range. The uncertainty in the atomic mass may exceed the stated value for such specimens.
Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.
Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC which use expanded uncertainties.

[edit] References

Isotope masses from Ame2003 Atomic Mass Evaluation by G. Audi, A.H. Wapstra, C. Thibault, J. Blachot and O. Bersillon in Nuclear Physics A729 (2003).
Isotopic compositions and standard atomic masses from Atomic weights of the elements. Review 2000 (IUPAC Technical Report). Pure Appl. Chem. Vol. 75, No. 6, pp. 683-800, (2003) and Atomic Weights Revised (2005).
Half-life, spin, and isomer data selected from these sources. Editing notes on this article's talk page.
- Audi, Bersillon, Blachot, Wapstra. The Nubase2003 evaluation of nuclear and decay properties, Nuc. Phys. A 729, pp. 3-128 (2003).
- National Nuclear Data Center, Brookhaven National Laboratory. Information extracted from the NuDat 2.1 database (retrieved Sept. 2005).
- David R. Lide (ed.), Norman E. Holden in CRC Handbook of Chemistry and Physics, 85th Edition, online version. CRC Press. Boca Raton, Florida (2005). Section 11, Table of the Isotopes.